Does take-off weight vary with latitude?

27 June 2010

Question

I know that the earth isn’t totally spherical. If mass stays the same but the gravity differs when moving from the midlatitudes towards the equator or polar region, how will it show for example when you take a Boeing 747 - how many percent can the measured weight differ compared when you take the mass from the pole to the equator?

Answer

Andrew - The strength of gravity on Earth is measured in terms of how fast it accelerates things and roughly speaking, it's about 10 metres per second every second. That's how fast it accelerates things. And you're absolutely right that it differs slightly depending on whether you're at the equator or at the poles, and there are basically two effects that are contributing to that. The first is actually the rotation of the Earth itself. We were saying earlier on that if you're standing on the poles, that point is fixed so you're not moving at all whereas if you're at the equator, you're moving very fast around it in a circle, and that reduces the gravity that you feel by what's actually 3.4 centimetres per second per second. So that's about a 0.3% effect. It reduces the weight by 0.3%. You also said correctly that the Earth actually bulges around the equator and I think if I'm getting this right, that's going to make it up into about a 0.5% effect. So it's going to have a 0.5% effect on the weight that's measured of your Boeing 747 which is not really a huge amount in terms of the uncertainties involved in aviation.

Chris - [With aviation] they've also taken into account extra things in terms of safety factors before those kind of take offs anyway. So it's already been taken account of.

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